1. Field of the Invention
The present invention relates to a seam construction for a papermaker's fabric, in general and, in particular, to a seam construction for a papermaker's dryer fabric.
2. Prior Art
The prior art has recognized for some time the advantages to be achieved in seaming a woven papermaker's fabric to form an endless belt for use in paper machines. In the dryer section of the papermaking machines, it has long been accepted practice to seam the fabric.
Various seam constructions will be known to those skilled in the art. One type of known seam is the clipper hook seam. In this type of seam, the hooks, generally of stiff wire, are affixed to each end of the fabric and the ends of the fabric are meshed together and a cable inserted to complete the seam.
Another known seam is the multifilament seam. In this seam, multifilament yarn connecting loops are woven into a webbing that has been sewed to the fabric body.
Another known seam is the spiral seam. This seam is generally formed of all plastic materials. Loops of a continuous spiral are affixed to either end of the fabric, the loops are intermeshed and interconnected with a pintle wire to form the seam.
Another known seam is the pin seam. In this construction, connecting loops of machine direction monofilament yarns are woven back into the fabric body. Generally, the back woven yarns are woven to complement the weave pattern of the fabric body. The loops are intermeshed and joined as a seam by a monofilament connecting pin or pintle.
Regardless of the seam construction utilized, it has been recognized by the art that the seam characteristics are critical to the performance of the fabric as a papermaker's fabric. Likewise, it has been recognized that the seam must resemble the body of the fabric as closely as possible. In addition, the seam must be uniform and lie flat within the plane of the papermaker's fabric. Although certain applications may be more tolerant of seam irregularities, which may cause marks on the paper, it is always desirable to eliminate inconsistencies between the seam and the fabric body.
The seam construction in fabrics utilized in the dryer section of the fabric has long been recognized as being critical. However, as higher speeds are attained in the papermaking machine, the seam becomes increasingly critical in forming fabrics and wet press felts. In addition to increased speed, the desire to continuously reduce the caliper of the fabric, regardless of the section in which it is utilized, has lead to additional pressures for a uniform seam within the fabric plane.
In addition to the need for uniform seams in higher speed and lower caliper fabrics, it has long been recognized that the connecting pin or pintle utilized in the seam is critical to the operation of the seam and the durability of the fabric in production.
Although a number of the above seams have been successful, there are some remaining limitations in the prior art seam constructions. As the fabric thickness or caliper is reduced, the thickness of the seam must be reduced so that the seam does not have a greater thickness or caliper than the fabric. Such an enlarged seam can lead to paper marking and reduced seam life. The desire to reduce seam caliper has lead to an associated reduction in the size or caliper of the seaming elements. In particular, the pintle element has been reduced, in some cases, to the lower limits of acceptability. This has resulted in premature seam failure which renders an otherwise useful fabric unproductive.
In view of the above, it is the general object of the present invention to provide an improved seam construction that is especially useful for lower caliper papermaker's fabrics. In particular, it is an object of this invention to provide a seam construction for fabrics of the type having two layers of cross machine direction yarns interwoven with a common single layer of machine direction yarns.